SpringMVC(二十五)：Servlet3.0+异步方法实现服务端的消息推送

star2017 1年前 ⋅ 352 阅读

Servlet 3.0+ 异步方法实现服务端消息推送是通过使用定时任务，定时的让控制器从另外一个线程返回一个DeferedResult并推送给客户端。而更新DeferedResult是在使用@Scheduled定时任务注解的方法里执行的。

示例

Maven管理的项目，pom.xml添加Servlet 3.0+版本依赖包。

  1. 在SpringMvcConfig.java类上添加开启定时任务的注解

     @Configuration
 @EnableWebMvc
 @EnableScheduling//开启计划任务
 @ComponentScan(basePackages = {"com"})
 public class SpringMvcConfig extends WebMvcConfigurerAdapter {

     /**
      * 配置viewResolver，用来映射来物理路径
      * @return
      */
     @Bean
     public InternalResourceViewResolver viewResolver() {
         InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();

         viewResolver.setPrefix("/WEB-INF/jsp/");
         viewResolver.setSuffix(".jsp");
         viewResolver.setViewClass(JstlView.class);
         return viewResolver;
     }

  2. Web初始化类时添加开启Servlet3.0+异步方法

     /**
  * WebApplicationInitializer是Spring提供用来配置Servlet+3.0配置的接口，从而实现了替代web.xml的位置。
  * 实现该接口会自动被SpringServletContainerInitializer(用来启动Servlet3.0容器)获取到。
  * @author Rocky
  *
  */

 public class WebInitializer implements WebApplicationInitializer {

     @Override
     public void onStartup(ServletContext servletContext) throws ServletException {

         //注解方式配置的web上下文
         AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
         context.register(SpringMvcConfig.class);
         //将上下文和当前servletContext关联
         context.setServletContext(servletContext);
         //注册dispatcher
         Dynamic servlet = servletContext.addServlet("dispatcher", new DispatcherServlet(context));
         servlet.addMapping("/");
         servlet.setLoadOnStartup(1);
         //Servlet3.0支持开启异步方法
         servlet.setAsyncSupported(true);
     }
 }

  3. Controller

     @Controller
 public class AysncController {

     @Autowired
     PushServiceImpl pushServiceImpl;

     @RequestMapping("/async")
     public String asyncPage() {
         return "async";
     }

     @RequestMapping("/defer")
     @ResponseBody
     public DeferredResult<String> deferredCall() {
         return pushServiceImpl.getAsyncUpdate();
     }
 }

  4. Service

     @Service
 public class PushServiceImpl {

     private DeferredResult<String> deferredResult;

     public DeferredResult<String> getAsyncUpdate(){
         deferredResult = new DeferredResult<>();
         return deferredResult;
     }

     //定时任务，每5秒执行一次
     @Scheduled(fixedDelay = 5000)
     public void refresh() {

         if(deferredResult != null) {
             SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
             String dateTime = sdf.format(System.currentTimeMillis());
             deferredResult.setResult("NowDateTime: " + dateTime);
         }
     }
 }

  5. jsp

     <%@ page language="java" contentType="text/html; charset=UTF-8"
     pageEncoding="UTF-8"%>
 <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

 <script type="text/javascript"
     src="${pageContext.request.contextPath}/static/js/jquery-1.11.0.js"></script>

 <script type="text/javascript">
     var s = '';
     deferred();

     function deferred() {

         $.get('defer', function(data) {
             console.log(data);
             s = s + (data + "<br/>");
             $("#msgFromPush").html(s);
             deferred();
         })
     }
 </script>

 <title>SSE Demo</title>
 </head>
 <body>
     <div id="msgFromPush"></div>
 </body>
 </html>

参考资料

Servlet 3特性：异步Servlet
tomcat servlet3的异步化原理理解

更多内容请访问：IT源点

注意：本文归作者所有，未经作者允许，不得转载

#消息推送 #异步 #Servlet
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